The present invention relates to an image-information format control device and more particularly to an image-information storage and communication system which realizes services for delivering and mailing audio visual information from the image-information storage device to any of a plurality of terminals over a communication network to which they are connected.
The terminals are classified into two groups having different source formats--CIF (Common Intermediate Format) and QCIF (Quarter CIF).
The CIF has a hierarchical structure including 4 hierarchies, i.e., frame, group of blocks (GOB), macro-block (MB) and block, and it represents such a source format that a luminance sample includes 352 pixels.times.288 lines per frame and a chrominance sample includes 176 pixels.times.144 lines.
The QCIF is reduced to 1/2 the number of pixels and lines respectively in comparison with the CIF.
The operation of the conventional image-information storage and communication system will be described below:
Data of each frame includes a picture start code (PSC), temporal reference (TR), type information (PTYPE), extra insertion information (PEI), spare information (PSPARE) (a set of the above-mentioned components is called a frame header) and following thereafter data of GOB. Each frame is divided into 12 GOB for the CIF format and 3 GOB for the QCIF format.
Data of each GOB includes a GOB start code (GBSC), group number (GN), quantizer information (GQUANT), extra insertion information (GEI), spare information (GSPARE) (a set of above-mentioned components is called as a GOB header) and following thereafter data of a macro-block (MB). Each GOB is divided into 33 MBs.
Data of each MB includes a macro-block address (MBA), type information (MTYPE), quantizer information (MQUANT), motion vector data (MVD), coded block pattern (CBP) (a set of the above-mentioned components is called a macro-block (MB)) and following thereafter block data. 1 MB is includes 4 blocks of luminance data and 2 blocks of chrominance data.
Data of one block includes a transform coefficient and a code EOB indicating the end of block marker. Data of a conversion coefficient includes 8.times.8 data.
In a situation where a terminal, which is capable of handling CIF format, or QCIF format requests the image-information storage device to transmit image-information, data transmitted from the terminal over the data channel are received by the receiving portion. The received data contain data indicating which format (CIF or QCIF) the terminal has and data indicating what kind of image information the terminal requires. The received data are then sent to the image-information storage device 8 through the interface portion thereof. The image-information storage device 8 holds data of image-information in two different formats, CIF and QCIF, and can transmit the requested image-information data in the format specified by the terminal.
Besides conventional interactive communication services such as a telephone, facsimile and so on, an audio delivery service, capable of storing audio-information in a center of networks and capable reproducing it any time it is requested, has recently been provided. With development of digital communication networks, which are represented by Integrated Services Digital Network (ISDN), it has also become possible to utilize image communication services, e.g., an audio visual service. In these circumstances, the demand for image-information delivery services increases more and more and such services have partly been realized.
In the conventional image storage and communication system, the same image is stored in two different formats, resulting in a considerable waste of memory. This is because if image-information data are stored in only one of the formats (i.e., CIF or QCIF), it becomes impossible to communicate with terminals having a different source format.
Furthermore, the conventional image-information reproducing system involves such a problem that in a case when image-information is stored in the format CIF in an image-information storage device at a network center, and a video data receiving terminal can decode video information of the QCIF format only, the image data stored in the CIF format cannot be transmitted from the center to the terminal.